On Tue, 2019-01-15 at 16:56 +0000, Daniel P. Berrangé wrote:
On Sun, Jan 13, 2019 at 06:12:06PM -0500, Cole Robinson wrote:
Add new <disk> model values for virtio transitional devices. When combined with bus='virtio':
* "virtio-transitional" maps to qemu "virtio-blk-pci-transitional" * "virtio-non-transitional" maps to qemu "virtio-blk-pci-non-transitional"
Signed-off-by: Cole Robinson <crobinso@redhat.com> --- src/qemu/qemu_command.c | 31 ++++++++++++++++++- src/qemu/qemu_domain_address.c | 2 ++ ...virtio-non-transitional.x86_64-latest.args | 7 +++-- .../virtio-transitional.x86_64-latest.args | 4 +-- .../virtio-non-transitional.xml | 10 ++++-- 5 files changed, 45 insertions(+), 9 deletions(-)
diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c index 822d5f8669..ca6abea227 100644 --- a/src/qemu/qemu_command.c +++ b/src/qemu/qemu_command.c @@ -443,6 +443,33 @@ qemuBuildVirtioDevStr(virBufferPtr buf, return 0; }
+static int +qemuBuildVirtioTransitional(virBufferPtr buf, + const char *baseName, + virDomainDeviceAddressType type, + bool transitional, + bool nontransitional) +{ + if (qemuBuildVirtioDevStr(buf, baseName, type) < 0) + return -1; + + if (type != VIR_DOMAIN_DEVICE_ADDRESS_TYPE_PCI && + (transitional || nontransitional)) { + virReportError(VIR_ERR_CONFIG_UNSUPPORTED, + _("virtio transitional models are not supported " + "for address type=%s"), + virDomainDeviceAddressTypeToString(type)); + return -1; + } + + if (transitional) { + virBufferAddLit(buf, "-transitional"); + } else if (nontransitional) { + virBufferAddLit(buf, "-non-transitional"); + } + return 0;
So this only works on QEMU >= 4.0.0 - earlier versions will fail to start.
We can, however, make it work correctly with old QEMU.
A transitional device is 100% identical to the existing device types, so we can simply not add the "-transitional" suffix for old QEMU. The only difference is the way libvirt does PCI bus placement of the transitional device - we'd never use PCIe.
A non-transitional device is identical to the existing device types, but with disable-legacy=true set.
Again, the relationship between existing and new devices is not quite this straighforward because of the reasons I outlined in https://www.redhat.com/archives/libvir-list/2019-January/msg00514.html But the idea of using disable-{legacy,modern} instead of the new virtio-*-{non,}-transitional devices is one I had already suggested in https://bugzilla.redhat.com/show_bug.cgi?id=1614127 so I'm obviously on board with it :)
QEMU guarantees this compatibility of the different devices, but only for machine types < pc-i440fx-4.0.0 / pc-q35-4.0.0. So we should none the less make sure we use the modern device names for any QEMU which genuinely supports them.
As I already mentioned in the bug report linked above, I'm not quite convinced that's the case, and I don't see why we wouldn't just use the options and basically ignore the QEMU-level devices, as the former approach would work on old QEMU releases as well as recent ones with no drawback I can think of. -- Andrea Bolognani / Red Hat / Virtualization